Substrate Holder for Graphene Film Synthesis

ABSTRACT

An apparatus and method for graphene film synthesis. The apparatus includes a quasi enclosed substrate holder which includes one open side, a cap disposed over the one open side of the quasi enclosed substrate holder, and a substrate for graphene film synthesis located inside the quasi enclosed substrate holder. The method includes placing a substrate for graphene film synthesis inside of a quasi enclosed substrate holder and generating a graphene film on the substrate via chemical vapor deposition, wherein the quasi enclosed substrate holder includes one open side and a cap disposed over the open side of the quasi enclosed substrate holder.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made with Government support under Contract No.:FA8650-08-C-7838 awarded by Defense Advanced Research Projects Agency(DARPA). The Government has certain rights in this invention.

FIELD OF THE INVENTION

Embodiments of the invention generally relate to electronic devices and,more particularly, to graphene film synthesis.

BACKGROUND OF THE INVENTION

Synthesis of graphene films on copper (Cu) foils by chemical vapordeposition (CVD) of hydrocarbons show promise for graphene production.However, existing approaches produce chemical vapor deposition graphenefilms that are polycrystalline with grain size typically less than 10micrometers. Such existing approaches attempt to optimize synthesisparameters such as, for example, temperature and hydrocarbon partialpressure.

Larger graphene grain size can be achieved at higher temperature andlower hydrocarbon partial pressure. However, disadvantages exist in thatthere are limitations on these parameters. For example, temperature islimited by the copper (Cu) melting point, and the hydrocarbon partialpressure cannot be too low to get effective growth. Accordingly, thegrain size of graphene is limited even with these noted optimizedparameters.

In this particular application, there is a need for large-grain graphenefilm synthesis techniques.

SUMMARY OF THE INVENTION

In one aspect of the invention, an apparatus for graphene film synthesisis provided. The apparatus includes a quasi enclosed substrate holderwhich includes one open side, a cap disposed over the one open side ofthe quasi enclosed substrate holder, and a substrate for graphene filmsynthesis located inside the quasi enclosed substrate holder.

Another aspect of the invention includes a method for generating agraphene film is provided. The method includes the steps of placing asubstrate for graphene film synthesis inside of a quasi enclosedsubstrate holder and generating a graphene film on to the substrate viachemical vapor deposition, wherein the quasi enclosed substrate holderincludes one open side and a cap disposed over the open side of thequasi enclosed substrate holder.

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof, which is to be read in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an overhead view of an example design,according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating a cross-section view of an exampledesign, according to an embodiment of the present invention;

FIG. 3 is a diagram illustrating graphene grain density, according to anembodiment of the present invention;

FIG. 4 is a diagram illustrating graphene grain density, according to anembodiment of the present invention;

FIG. 5 is a diagram illustrating graphene grain density, according to anembodiment of the present invention; and

FIG. 6 is a flow diagram illustrating techniques for generating agraphene film, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

An aspect of the invention includes a quasi-enclosed substrate holderfor large-grain graphene film synthesis by chemical vapor deposition(CVD). As used herein, large-grain graphene film can include graphenefilm of more than hundreds of micrometers in length. Other chemicalvapor deposition grown graphene, such as those in existing approaches,generally has grain size in the order of several to tens of micrometers.

As noted herein, chemical vapor deposition grown graphene films arepolycrystalline, and grain boundaries as well as intrinsic topologicaldefects of polycrystalline materials can markedly alter the electronictransport in graphene. By way merely of example, description of grainboundaries and topological defects affecting electronic transport can befound in Yu et al., Control and characterization of individual grainsand grain boundaries in graphene grown by chemical vapour deposition,Nature Materials 10, 443 (2011), and Li et al., Letter Graphene Filmswith Large Domain Size by a Two-Step Chemical Vapor Deposition Process,Nano Lett. 10, 4328 (2010). Also, graphene grain size is affected bytemperature, hydrocarbon flow rate and partial pressure.

By way merely of example, graphene grains grown on the inside of acopper enclosure are found to be much larger than those grown on theoutside of such an enclosure. The copper foil enclosure is customarilyformed, in such existing approaches, by bending the copper foil,followed by crimping the three remaining sides. Such an approach,however, is not scalable because with the increase of grain size, thefoil enclosure may collapse, thereby causing the two walls of theenclosure to stick to each other.

Accordingly, an aspect of the present invention includes a scalablequasi enclosed substrate holder in which the copper (Cu) foils are usedfor graphene growth rather than putting the Cu foils directly in the CVDchamber. In at least one embodiment of the invention, copper foils areused as the substrate because copper can be the same material as is usedfor the cover. Accordingly, the vapor of the cover will not interferewith the reaction. However, as should be appreciated by one skilled inthe art, any inert material can be used as the substrate in accordancewith at least one embodiment of the invention. By way of example, suchan inert material that can be used for the substrate can include quartz.

As detailed herein, the graphene films grown on the copper foils in thequasi enclosed substrate holder (also referred to herein as a box) havemuch larger grain size than those grown on copper foils put directly inthe CVD chamber. Accordingly, the larger grain size growth isfacilitated by the ability of gases to move in and out of the quasienclosed substrate holder (box), albeit move in and out of the substrateholder at a low efficiency.

In one embodiment of the invention, the substrate holder for a coppersubstrate for graphene growth is a prolate quartz box with one-sideopen. In at least one embodiment of the invention, other hightemperature (resistant) (for example, greater than 1000 degrees Celsius)inert materials can be used as a material for the substrate holder. Byway of example, such inert materials that can be used for the substrateholder can include sapphire or alumina. The size of the gap (that is,the opening on the one open side of the box) can be of any reasonablerange because the gap will ultimately be covered by the cap. In apreferred embodiment of the invention, however, the gap has a width of arange from approximately 1 millimeters (mm) to 2 mm. An embodiment ofthe invention additionally includes a substrate holder that includes acap made of a metal foil, as additionally detailed herein.

FIG. 1 is a diagram illustrating an overhead view of an example design,according to an embodiment of the present invention. By way ofillustration, FIG. 1 depicts a three-dimensional (3D) overhead view 102including the following components. Accordingly, FIG. 1 depicts aprolate quartz box 100 with one-side open. The gap for the open side isa width of a range from approximately 1 to 2 mm. Length and width of thebox are determined (or limited) by the CVD chamber size. In other words,the box must be small enough to put into the CVD chamber, but there neednot be a preferred size ratio therewith.

As also depicted in FIG. 1, cap 110, disposed over the one open side ofbox 100, is made of a metal foil (for example, copper). In at least oneembodiment of the invention, copper foils are used as the cap/coverbecause copper can be the same material as is used for the substrate forgraphene growth. In such an embodiment of the invention, the vapor ofthe cover will not interfere with the reaction. However, as should beappreciated by one skilled in the art, any inert material can be used asthe cover in accordance with at least one embodiment of the invention.By way of example, such an inert material that can be used for the covercan include quartz. In an embodiment of the invention, as noted, the capshould be the same metal as the substrate used for graphene growth.

As detailed further herein, in an aspect of the invention, the capcompletely covers the open side but does not form a seal. Thus, gasescan still go in and come out but with low efficiency.

As further depicted in FIG. 1, copper substrate 120, located inside theopen-sided box 100, is for graphene growth.

FIG. 2 is a diagram illustrating a cross-section view of an examplequasi enclosed substrate holder design, according to an embodiment ofthe present invention. By way of illustration, FIG. 2 depicts across-section view 104 including the same components as depicted in theoverhead view of FIG. 1. Accordingly, FIG. 2 depicts a prolate quartzbox 100 with one-side open, a cap 110, disposed over the one open sideof box 100, and a substrate 120, located inside the open-sided box 100,for graphene growth. As noted above and again illustrated in FIG. 2, thecap 110 completely covers the open side of the box 100, but does notform a seal, allowing gases to move in and out of the box 100, albeitwith low efficiency.

FIG. 3 is a diagram illustrating graphene grain density, according to anembodiment of the present invention. By way of illustration, FIG. 3depicts an illustration 202 of normal growth (that is, copper foilsdirectly put into the CVD chamber).

Additionally, FIG. 4 is a diagram illustrating graphene grain densityinformation, according to an embodiment of the present invention. By wayof illustration, FIG. 4 depicts an image 204 representative of graphenegrown on the inside surface of a copper enclosure.

FIG. 5 is a diagram illustrating graphene grain density, according to anembodiment of the present invention. By way of illustration, FIG. 5depicts an illustration 206 of graphene grown on a copper substrateinside of a quasi enclosed box, as described herein.

It can be seen in FIG. 3 through FIG. 5 that graphene grain density ismuch smaller for the case of a copper enclosure 204 depicted in FIG. 4and the quasi enclosed box 206 depicted in FIG. 5 than the normal growthillustration 202 depicted in FIG. 3. Accordingly, as further detailedherein, the use of the quasi enclosed box produces graphene films withmuch larger grain size, wherein grain size is the reciprocal of graindensity.

FIG. 6 is a flow diagram illustrating techniques for generating agraphene film, according to an embodiment of the present invention. Step602 includes placing a substrate for graphene film synthesis inside of aquasi enclosed substrate holder. The quasi enclosed substrate holderincludes one open side and a cap disposed over the open side of thequasi enclosed substrate holder. The quasi enclosed substrate holder isscalable and can include a high temperature (resistant) inert material.By way of example, the substrate holder can be a prolate quartz box withone open side. As used herein, that the quasi enclosed substrate holderis scalable refers to the fact that the length and width of thesubstrate holder can be multiple sizes while keeping the gap sizeunchanged. Accordingly, a quasi enclosed substrate holder such asdetailed herein can be used for copper foils of any size.

The cap (or cover) placed over the open side of the quasi enclosedsubstrate holder can be made of an inert material. By way of example,the cap can be a metal foil (for example, copper). The quasi enclosedsubstrate holder includes one open side, that is, a gap having a widthin the range of from about 1 mm to 2 mm. Additionally, in at least oneembodiment of the invention, the quasi enclosed substrate holder has alength and a width determined by a chemical vapor deposition chambersize. For example, the quasi enclosed substrate holder, in suchembodiments, can be as long and as wide so as to still permit thesubstrate holder to fit inside the particular chemical vapor depositionchamber.

Step 604 includes generating a graphene film on the substrate viachemical vapor deposition. By way of example, in the traditionalchemical vapor deposition process, the substrate is put into thechemical vapor deposition chamber directly and exposed to a gas flow.Thus, the dynamic flow parameters (for example, gas flow rate andgeometry, and dimensions of the CVD chamber) may also affect graphenegrowth. In an aspect of the invention, however, within the box, thegases are quasi static. Molecules move only by diffusion, thus leadingto larger graphene domain size by using the quasi-enclosed box. In atleast one embodiment of the invention, the cap/cover should fit astightly as possible over the quasi enclosed substrate while stillpermitting gases to move in and out of the holder.

Additionally, the substrate, as described herein, can be an inertmaterial. By way of example, the substrate can be a metal foil (forexample, copper). Graphene films synthesized according to at least oneembodiment of the invention have larger domain size and thus less domainboundaries. This is, in existing approaches, one of the main defectsdegrading graphene quality on their mechanical strength and thermal andelectrical transport properties. In other words, larger domain graphenefilms have higher quality.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may bemade by one skilled in the art without departing from the scope orspirit of the invention.

What is claimed is:
 1. An apparatus for graphene film synthesis,comprising: a quasi enclosed substrate holder which includes one openside; a cap placed over the one open side of the quasi enclosedsubstrate holder; and a substrate for graphene film synthesis locatedinside the quasi enclosed substrate holder.
 2. The apparatus of claim 1,wherein the quasi enclosed substrate holder is scalable.
 3. Theapparatus of claim 1, wherein the quasi enclosed substrate holdercomprises a prolate quartz box with one open side.
 4. The apparatus ofclaim 1, wherein the quasi enclosed substrate holder comprises a hightemperature inert material.
 5. The apparatus of claim 1, wherein the oneopen side of the quasi enclosed substrate holder includes a gap having awidth in the range of from about 1 mm to 2 mm.
 6. The apparatus of claim1, wherein the quasi enclosed substrate holder has a length and a widthdetermined by a chemical vapor deposition chamber size.
 7. The apparatusof claim 1, wherein the cap placed over the open side of the quasienclosed substrate holder is made of an inert material.
 8. The apparatusof claim 1, wherein the cap placed over the open side of the quasienclosed substrate holder is made of a metal foil.
 9. The apparatus ofclaim 8, wherein the metal foil comprises a copper foil.
 10. Theapparatus of claim 1, wherein the substrate is an inert material. 11.The apparatus of claim 1, wherein the substrate is a metal foil.
 12. Theapparatus of claim 11, wherein the metal foil comprises a copper foil.13. A method for generating a graphene film, comprising: placing asubstrate for graphene film synthesis inside of a quasi enclosedsubstrate holder; and generating a graphene film on the substrate viachemical vapor deposition; wherein the quasi enclosed substrate holderincludes: one open side; and a cap disposed over the open side of thequasi enclosed substrate holder.
 14. The method of claim 13, wherein thequasi enclosed substrate holder comprises a prolate quartz box with oneopen side.
 15. The method of claim 13, wherein the quasi enclosedsubstrate holder comprises a high temperature inert material.
 16. Themethod of claim 13, wherein the one open side of the quasi enclosedsubstrate holder includes a gap having a width in the range of fromabout 1 mm to 2 mm.
 17. The method of claim 13, wherein the quasienclosed substrate holder has a length and a width determined by achemical vapor deposition chamber size.
 18. The method of claim 13,wherein the cap placed over the open side of the quasi enclosedsubstrate holder is made of an inert material.
 19. The method of claim13, wherein the cap placed over the open side of the quasi enclosedsubstrate holder is made of a metal foil.
 20. The method of claim 19,wherein the metal foil comprises a copper foil.
 21. The method of claim13, wherein the substrate is an inert material.
 22. The method of claim13, wherein the substrate is a metal foil.
 23. The method of claim 22,wherein the metal foil comprises a copper foil.
 24. The method of claim13, wherein the quasi enclosed substrate holder is scalable.